TECHNICAL FIELD
1. Field of the Invention
This invention relates to picture transmission techniques, e.g. television systems using, in particular, line-by-line or interlaced scanning, and is, more specifically, concerned with devices for data display.
2. Description of the Related Art
Known in the art is a device for display of information (U.S. Pat. No. 2,678,964), comprising a high-frequency amplifier, a frequency converter, an intermediate frequency amplifier, a video detector, a video amplifier, a sound channel, line and frame generators, a picture tube featuring a deflection system, and some other additional units intended to improve the sharpness of the picture. In this prior art device, the sharpness of the picture is achieved by slowing down the speed of the line scanning, when reproducing the image outlines, or, in other words, in response to any fast changes in the brightness of the picture. To this end, the device additionally comprises several series-connected units, such as an image contour detector, an output amplifier, and one more line deflecting coil (apart from the coil of the deflection system) or line deflecting plates. In this device, the input of the image contour detectors is connected to the output or input of the video amplifier. This image contour detector comprises one or two differentiating circuits and may include a signal level limiter.
The disadvantage of this data display device consists in that the enhancement in the sharpness of the picture is not substantial. This is due to the non-rectangular shape of the signal produced by the image contour detector. Since the duration of this signal is equal to the duration of the edge of the video signal from which it is produced, this signal has an intricate shape containing several alternating halfwaves. The scanning beam is therefore arrested for only a part of the duration of the video signal edge and not for the complete duration thereof.
Known in the art is a data display system (U.S. Pat. No. 4,080,628) comprising a high frequency amplifier, a frequency converter, an intermediate frequency amplifier, a video detector, a video amplifier, a sound channel, line and frame generators, a picture tube with a deflection system, an image contour detector, an output amplifier, and one more line deflection coil (in addition to the coil in the deflection system) or line deflection plates. In the image contour detector, the output signal is produced by differentiating the video signal, full wave limitation of this video signal, summing the limited signal with the initial video signal, and subsequent second differentiation of the obtained sum. This signal is supplied, via an output amplifier, to horizontal deflecting plates or horizontal deflection coils.
This known system is deficient in that the scanning beam is arrested, to display the image edges, only for a period much shorter than the duration of a respective edge of the video signal. The enhancement of the sharpness of the picture is therefore not substantial.